BN/BO Doping of peri‐Acenoacenes: Modulating Excited States in Trapeziumene Congeners

TL;DR

Researchers synthesized new aromatic hydrocarbons with boron, nitrogen, and oxygen to control their light-emitting and electronic properties.

Contribution

A new class of doped aromatic hydrocarbons is synthesized with tunable excited-state properties via peripheral doping.

Findings

Peripheral doping patterns modulate π-conjugation and intermolecular packing in trapeziumene congeners.

N→O substitution increases S1 energy and widens the T2–T1 energy gap, altering fluorescence and phosphorescence.

The compounds show bright fluorescence and p-type electrochemical behavior with tunable HOMO–LUMO gaps.

Abstract

The rational design of polycyclic aromatic hydrocarbons that combine chemical and physical robustness with finely tuned optoelectronic properties remains a key challenge in materials science. As an initial step toward this goal, we report the synthesis and comprehensive characterization of a new class of boron‐, nitrogen‐, and oxygen‐doped peri‐acenoacenes, termed (2,5,4)‐trapeziumene congeners. Analysis of these systems provides chemical descriptors that could guide the rational tailoring of their properties through peripheral doping. The target trapeziumene congeners were obtained via a sequence of Suzuki–Miyaura and Buchwald–Hartwig couplings, followed by directed borylation, giving both phenylborane and borinic derivatives with diverse peripheral doping sequences. Single‐crystal X‐ray diffraction revealed planar to slightly twisted backbones, with peripheral heteroatomic motifs that modulate π‐conjugation and intermolecular packing. Photophysical studies showed bright fluorescence (Φ
F up to 0.99), narrow Stokes shifts, and structured phosphorescence at 77 K. Electrochemical analysis demonstrated p‐type behavior and a progressive HOMO–LUMO gap widening upon N→O substitution. Theoretical investigations revealed that N→O substitution asymmetrically affects the excited states, blue‐shifting fluorescence while red‐shifting phosphorescence, through an asymmetric charge stabilization in the S1 and T1 excited states. This is accompanied by a progressive widening of the T1–T2 energy gap.

A new family of (2,5,4)‐trapeziumenes bearing NBNBN, NBOBN, OBNBO, and OBOBO doping patterns is synthesized. Progressive N→O substitution enables precise control over the excited‐state landscape, increasing the S1 energy, decreasing the T1 energy, and widening the T2–T1 energy gap.

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